(ii) That it is possible to produce and correct roll and yaw by unreversed use of the rolling and directional control.
(iii) The amount of roll or yaw encountered during the recovery.
(4) Speed Reduction Rate. Section 23.201(b) requires the rate of speed reduction for entry not exceed one knot per second.
c. Data Acquisition and Reduction.
(1) Instruments. The applicant should provide a recently calibrated sensitive altimeter, airspeed indicator, accelerometer, outside air temperature gauge, and appropriate propulsion instruments; such as a torque meter or manifold pressure gauge and tachometer, a means to depict roll, pitch, and yaw angles; and force gauges when necessary.
(2) Data Recording. Automatic data recording is desirable, but not required, for recording time histories of instrumented parameters and such events as stall warning, altitude loss, and stall break. The analysis should show the relationship of pitch, roll, and yaw with respect to various control surface deflections. (See figure 17-1, stall speed determination.)
d. Stick Pusher.
(1) Background. Stick pushers have been installed in some airplanes that would not meet the requirements of § 23.201. This was accomplished under the provisions of § 21.21b(1). In some airplanes, operation of the stick pusher was not critical to safe flight and, in others, stick pusher performance was essential to safe flight. In the latter case, the stick pusher typically functions as a stall barrier to prevent an airplane from entering flight regimes where a nonrecoverable stall could occur.
(2) Stall Prevention. There are two basic situations where a stick pusher would be necessary to show compliance with regulations. These are the following:
(i) Airplane Recoverable. The stall characteristics are investigated and, during these tests, the airplane does not meet regulatory requirements but an inadvertent aerodynamic stall would not be catastrophic or require exceptional piloting skill to recover. For example, during certain conditions of c.g., weight, or power, the airplane exceeds the l5 degree roll limit because of excessive angle-of-attack or other conditions. The pusher is installed and designed to function at some angle-of-attack where the 15 degrees of roll will not be exceeded. If this pusher system fails to function, the airplane is still recoverable from the stalled flight condition. For this system, the occurrence of a failure should be evaluated for an unsafe condition.
(ii) Airplane Not Recoverable. When the airplane is not capable of recovering from stalls or the applicant chooses not to investigate the consequences of stalling demonstrations with the pusher system rendered inoperative, then if the stick pusher fails to perform its intended function, an unsafe condition would exist.
(3) System Tolerances. Stick pusher system(s) tolerances should be evaluated and accounted for during certification flight tests. The applicant normally specifies the system tolerances in terms of plus or minus so many knots. The system(s) should be set to the minus (lowest stall speed) side of the tolerance when investigating stall characteristics and minimum longitudinal trim capability. The system(s) should be set to the plus (highest stall speed) side of the tolerance for stall speed determination and for determining performance stall speed multiples.
Alternately, a nominal stick pusher stall speed may be used when it is determined that stick 84
pusher tolerances result in no more than 3 knots or 5 percent variation in stall speed, whichever is greater.
(4) Airspeed Margins. The airspeed margin between unsatisfactory stall characteristics and the minimum stick pusher actuation speed, for identical flight conditions, should be evaluated. The following information is provided as a guide. For airplanes with unsatisfactory, hazardous or unrecoverable aerodynamic stall characteristics, the minimum speed margin between aerodynamic stall and minimum stick pusher systems actuation speed should not be less than 5 knots. For other airplanes with known and less hazardous aerodynamic stall characteristics, the speed margin may be reduced to not less than 2 knots.
(5) Preflight Check. If a reliability credit is to be given for a preflight check, the following should be evaluated:
(i) The check includes the functioning of the complete system, including the incidence sensors, so all faults would be detected.
(ii) The check is easily conducted, and requires little pilot time or effort.
(iii) A note in the limitations section of the AFM requires the check to be accomplished prior to flight.
(iv) The AFM identifies the criticality of the system and the need to accomplish the preflight check.
(6) Inadvertent Operation. Inadvertent stick pusher operation should be extremely improbable or investigated and shown not to be hazardous and to be recoverable.
87. SECTION 23.203 TURNING FLIGHT AND ACCELERATED TURNING STALLS.
a. Explanation.
(1) Explanations 86.a.(2) and (4) for wings level stalls also apply to turning flight and accelerated turning stalls.
(2) The only differences between the investigation required for turning flight and accelerated turning stalls are in the speed reduction rate and the accepted roll off bank angles.
b. Procedures.
(1) Procedure 86.b.(1) for wings level stalls applies to turning flight and accelerated turning stalls.
(2) During the maneuver, the test pilot should determine the following:
(i) That the stick force remains positive up to the stall;
(ii) That the altitude lost is not, in the test pilot's opinion, excessive;
(iii) There is no undue pitch up;
(iv) That there are no uncontrollable spinning tendencies; that is, while the airplane may have a tendency to spin, a spin entry is readily preventable;
(v) That the test pilot can complete the recovery with normal use of the controls and average piloting skill;
(vi) Roll does not exceed the value specified in the requirements; and
(vii) For accelerated turning stalls, maximum speed or limit load factors were not exceeded.
(3) Section 23.203(a) requires the rate of speed reduction for a turning flight stall not exceed one knot per second; for an accelerated turning stall, 3 to 5 knots per second with steadily increasing normal acceleration.
c. Data Acquisition. Same as for wings level stalls.
88. SECTION 23.205 RESERVED
89. SECTION 23.207 STALL WARNING.
a. Explanation.
(1) Purpose. The purpose of this requirement is to ensure an effective warning in sufficient time to allow a pilot to recover from an approach to a stall without reaching the stall.
(2) Types of Warning. The effective warning may be from either aerodynamic disturbances or from a reliable artificial stall-warning device such as a horn or a stick shaker. The aerodynamic warning is usually manifested by a buffet, which vibrates or shakes the airplane.
The type of warning should be the same for all configurations.
(3) Artificial Stall Warning. Stall warning devices may be used in cases where there is inadequate aerodynamic warning. The warning signal from the devices should be clear and distinctive and not require the pilot's attention to be directed inside the airplane. A stall warning light by itself is not acceptable. If a stick shaker is installed, the warning should be unmistakable even if flying hands off.
b. Procedures. The stall warning tests should be conducted in conjunction with the stall tests required by §§ 23.201 and 23.203.
90.-99 RESERVED.
Section 8. SPINNING
100. SECTION 23.221 SPINNING.
a. Explanation.
(1) Spin. A spin is a sustained autorotation at angles-of-attack above stall. The rotary motions of the spin may have oscillations in pitch, roll, and yaw superimposed upon them.
The fully developed spin is attained when the trajectory has become vertical and the spin characteristics are approximately repeatable from turn to turn. Some airplanes can autorotate for several turns, repeating the body motions at some interval, and never stabilize. Most airplanes will not attain a fully developed spin in one turn.
(2) Category Spins. Section 23.221 addresses three situations:
(i) Normal category spins.
(ii) Utility category spins.
(iii) Acrobatic category spins.
(3) Reserved.
(4) Utility Category Airplanes. Utility category is used for airplanes intended for limited acrobatic operations in accordance with § 23.3. Spins (if approved for the particular type of airplane) are considered to be a limited acrobatic operation. This type of airplane may be approved in accordance with § 23.221(a), normal category, or with § 23.221(c), acrobatic category.
b. Discussion and Procedures Applicable to Both Normal and Acrobatic Category Spins.
(1) Weight and C.G. Envelope. See paragraph 7.a. of this AC for discussion of weight and
c.g. envelope exploration.
(2) Moments of Inertia. Moments of inertia should also be considered when evaluating the
c.g. envelope. Most general aviation airplanes have low inertias combined with high aerodynamic damping and relatively similar moments of inertia along the wing and fuselage axis. However, designs of modifications, such as wingtip fuel tanks, can change the spin recovery time and possibly the recovery method. Applicants are encouraged to consider these effects and approach flight testing at extreme mass distributions with caution.
(3) Control Deflections. Control surface deflections should be set to the critical side of the allowable tolerances for the selected critical configurations. For example, a possible spin flight test program could be to perform the spin matrix with the controls set at the nominal deflection values. Analysis of the data will show the critical conditions for entry and recovery. Once the critical conditions are defined and agreed upon by the Certification Authority, these critical tests are repeated with the control deflections set to the most critical tolerances. If satisfactory, these tests must be repeated with the antispin system removed.
(4) Emergency Egress. It is the responsibility of the applicant to provide adequate provision for crew restraint, emergency egress, and use of parachutes (reference § 21.35(d)).
(5) Spin Recovery Parachutes.
(i) Spin recovery parachutes should be installed on all airplanes requiring spin testing for certification.
(ii) The anti-spin system installation should be carefully evaluated to determine its structural integrity, reliability, susceptibility to inadvertent or unwanted deployment or jettison, and adequate or redundant jettison capability. NASA recommendations should be referred to when evaluating the design of the chute deployment and jettison systems.
The chute type, diameter, porosity, riser length, and lanyard length should be determined in accordance with NASA recommended practices to maximize the probability the chute will be effective in spin recovery. Chute sizes, and particularly riser and lanyard lengths, depend strongly on such aircraft variables as wing design, fuselage shape, tail arm, and mass properties. The sizes and lengths shown in the referenced NASA reports are for 87
particular aircraft that were tested in the NASA Langley Spin Tunnel and will not necessarily be the correct size to recover other aircraft, even if the aircraft layout is similar. Appropriate NASA recommendations can be found in the following publications:
(A) NASA Technical Paper 1076, "Spin-Tunnel Investigation of the Spinning Characteristics of Typical Single-Engine General Aviation Airplane Designs," dated November 1977.
(B) NASA Technical Note D-6866, "Summary of Design Considerations for Airplane Spin-Recovery Parachute Systems."
(C) NASA Conference Paper, CP-2127, l4th Aerospace Mechanisms Symposium, May 1980, entitled, "A Spin-Recovery System for Light General Aviation Airplanes."
The NASA documents are available from:
National Technical Information Service (NTIS) 5285 Port Royal Road Springfield, Virginia 22161
(iii) Final certification of the spin characteristics should be conducted with the external spin chute removed unless it is determined that spin chute installation has no significant effect on spin characteristics.
(6) Build-Up. When any doubt exists regarding the recovery characteristics of the test airplane, a build-up technique should be employed consisting of spin entries and recoveries at various stages as the maneuver develops. Excessive aerodynamic control wheel back pressure indicates a possibility of unsatisfactory spin characteristics. Any control force lightening or reversal is an indication of possible deep stall entry. See subparagraph c(7) for definition of excessive back pressure. A yaw rate instrument is valuable in detecting progress toward a fully developed spin condition or an uncontrollable maneuver. Unusual application of power or controls has sometimes been found to induce uncontrollable spins. Leading with elevator in recovery and cutting power as the airplane rolls into a spin have been known to induce uncontrollable spins.
(7) Entry. Spins should be entered in the same manner as the stalls in §§ 23.201 and 23.203 with trim at 1.5 VS1 or as close as practical. As the airplane stalls, with ailerons neutral, apply full-up elevator and full rudder in the direction of spin desired. Refer to paragraphs l00c and l00d for further discussion of spin entries.
(8) Recovery. Recoveries should consist of throttle reduced to idle, ailerons neutralized, full opposite rudder, followed by forward elevator control as required to get the wing out of stall and recover to level flight. For acrobatic category spins, the manufacturer may establish additional recovery procedures, provided they show compliance for those procedures with this section.
(9) Trimmable Stabilizer. For airplanes that trim with the horizontal stabilizer, the critical positions should be investigated.
(10) Altitude. The effect of altitude should be investigated.
(11) Initial Investigation. In all cases, the initial spin investigation should be accomplished at as high an altitude above the ground as reasonably possible and a predetermined, pre-briefed "hard" altitude established to be used as the emergency egress altitude. In other words, if the airplane cannot be recovered by that altitude, all occupants should exit the airplane without hesitation. The altitude selected should take into account the opening characteristics of the parachutes, the difficulty of egress, the estimated number of turns to get out and the altitude loss per turn, the distance required to clear the airplane before deploying the parachutes, and so forth.
(12) Power. The use of power for spin entry for both normal and abnormal control use is recommended in order to determine the effects of power on spin characteristics and spin recovery procedures. For power on normal category spins, the throttle can be reduced to idle after one turn.
c. Discussion and Procedures Applicable to Normal Category Spins.
(1) Objective. The basic objective of normal category spin testing is to assure that the airplane will not become uncontrollable within one turn (or 3 seconds, whichever takes longer) if a spin should be encountered inadvertently and that recovery can be effected without exceeding the airplane design limitations. Type certification testing requires recovery capability from a one-turn spin while operating limitations prohibit intentional spins. This one-turn "margin of safety" is designed to provide adequate controllability when recovery from a stall is delayed. Section 23.221(a) does not require investigation of the controllability in a true spinning condition for a normal category airplane. Essentially, the test is a check of the controllability in a delayed recovery from a stall.
(2) Recovery from Spins with Normal Control Usage During Entry and Recovery. Normal category airplanes must recover from a spin in no more than one turn after the initiation of the first control action for recovery. For example, if you are spinning left with ailerons neutral, recover by reducing power to idle, if not already at idle, apply full right rudder followed by forward elevator. Start the count (heading, ground reference, and so forth) for recovery with the application of the first action, which may be the reduction of power. See subparagraph c(5) for use of flaps. Intentional, inadvertent, normal, up to 60 degrees bank, and accelerated stalls should be considered.
(3) Recovery from Spins Following Abnormal Control Usage. Abnormal control usage should be evaluated during the spin to ensure that uncontrollable spins do not occur. The intent of these tests is to induce all of the types of control usage, whether they are right or wrong, that might be used during the operation of the airplane. The parameters that need to be investigated depend on the design of the airplane as well as on the results of the Normal Spin Tests. These checks include, as a minimum, the following: the effect of ailerons with and against the spin, the effect of elevator applied before the rudder at recovery, the effect of slow elevator release, the effect of entry attitude, the effect of power on at the entry, and the effect of power left on during the spin. Ailerons with and against the spin should be applied at entry and during spins. Elevator and rudder against the spin should be applied during the spin. Spinning should continue for up to 3 seconds, or for one full turn, while the effects of abnormal aerodynamic control inputs are observed. Apply normal recovery controls as outlined in subparagraph c(2). Up to two turns for recovery is considered acceptable.
(4) Spin Matrix. The effects of gear, flaps, power, accelerated entry and control abuse should be investigated. A suggested matrix for spin investigation is given in Figure 100-1. It is the responsibility of the applicant to explore all critical areas. It may be possible to eliminate the need to conduct some of the additional conditions once the airplane responses are known.
(5) Flaps. Section 23.221(a) specifies that, for the flaps extended condition, the flaps may be retracted during the recovery. Flap retraction should not be initiated until after airplane rotation has ceased.
(6) Aerodynamic Back Pressure. Excessive aerodynamic back pressure is cause for noncompliance. Excessive aerodynamic back pressure is a judgment item and is defined as excessive force required to pitch the airplane down in recovery. Back pressure should not be more than normal elevator control forces and should not interfere with prompt and normal recovery.
d. Discussion and Procedures Applicable to Acrobatic Category Spins.
(1) Objective. The basic objective of acrobatic category spin testing is to ensure that the airplane will not become uncontrollable when a spin is intentionally entered and the following:
(i) The controls are used abnormally (as well as normally) either during the entry or during the spin, or both;
(ii) The airplane will recover in not more than 1 1/2 turns after completing application of normal or manufacturer-prescribed recovery controls; and
(iii) No airplane limitations are exceeded, including positive maneuvering load factor and limit speeds.
(2) Pilot Training. It is assumed that the pilot of the acrobatic category airplane that spins for six turns is doing so intentionally. If spinning is intentional, the pilot should have had proper instruction and proficiency to effect a proper recovery. The pilot should be expected to follow the published procedure to recover from this planned maneuver.
(3) Abnormal Control Usage. The discussion of "abnormal" use of controls in paragraph l00c(3) also applies to acrobatic category spins. Abnormal control usage should be evaluated at several points throughout the spin to ensure that uncontrollable spins do not occur. These checks include, as a minimum, the following: the effect of ailerons with and against the spin, the effect of elevator applied before the rudder at recovery, the effect of slow elevator release, the effect of entry attitude, the effect of power on at the entry, and the effect of power left on during the spin. Spinning should continue for up to six full turns while the effects of abnormal aerodynamic control inputs are observed. The effect of leaving power on in the spin need only be examined by itself up to one full turn. Following abused control usage, reversion to normal pro-spin controls for up to two turns is acceptable, prior to the normal recovery control inputs, which must result in recovery in not more than two turns. In addition, going directly from the control abuse condition to the normal recovery control condition should not render the spin unrecoverable. For example, after evaluating the effect of relaxing the back stick input during the spin, it would be reasonable to expect the pilot to apply normal recovery use of rudder and elevator without first returning to full back stick.
(4) Flaps. If an acrobatic category airplane is placarded against intentional flaps down spins, then only normal category procedures need be used for the flaps down configurations.
(5) Spin Matrix. The effects of gear, flaps, power, accelerated entry, and normal and abnormal control use should be investigated. A suggested matrix for spin investigation is given in figure 100-1. It is the responsibility of the applicant to explore all critical areas. It is necessary to expand the matrix to cover six-turn spins. The normal procedure is to continue 90
the same process and add one additional turn each time. It may be possible to eliminate the need to conduct some of the additional conditions once the airplane responses are known.
(6) Spiral Characteristics. The acrobatic spin requirement stipulates that, for the flap retracted six-turn spin, the spin may be discontinued after 3 seconds if spiral characteristics appear. This does not mean that the spin test program is discontinued. Each test point should stand alone and that spin be discontinued only after a spiral has developed. Limit speed should not be exceeded in the recovery. The airplane may be certificated as an acrobatic airplane whether or not it can spin a minimum of six turns.
(7) Recovery Placard. Section 23.1583(e)(4) requires that acrobatic airplanes have a placard listing the use of controls required to recover from spinning maneuvers. Utility category airplanes approved for spins should also have such a placard. Recovery control inputs should be conventional. If special sequences are employed, then they should not be so unique to create a recovery problem.
(8) Complex Instrumentation. When complex instrumentation is installed, such as wing tip booms or a heavy telemetry system, the instrumentation may affect the recovery characteristics. Critical spin tests should be repeated with the instrumentation removed.
e. Data Acquisition. The test airplane should be equipped with a calibrated airspeed indicator, accelerometer, and altimeter. Precise control of weight and balance and control deflections is essential.
f. Optional Equipment. In those cases where an airplane is to be certified with and without optional equipment such as deicing boots, asymmetric radar pods, outer wing fuel tanks, or winglets, sufficient tests should be conducted to ensure compliance in both configurations.
Flight Condition Spins from Wing Level Attitude Spin Number Flaps Up Flaps Appch. (As Approp.)
Test with Normal Spin Controls Left Spin 1 thru 6 1 2 3 4 5 6 X X 7 8 9 10 11 12 13 14 15 16 17 18 Test with Abnormal Spin Controls Left Spin Aileron Against 7 thru 12 (Repeat 7 through 12 from a right spin) Left Spin Aileron with 13 thru 18 Flaps Landing Gear Up Gear Down Cowl Flaps Closed Cowl Flaps As Required Power Off Power On Forward C.G.
Aft C.G.
Lateral C.G.
X X X X X X X X X X X X X X X X X X X X XX X X X X XX XX XX Repeat 1 through 6 from a right spin.
Repeat 1 through 6 fromleft and right turning flight.
X X XXX X X
XX X XX X X
XX XX X X X
X X X XX X X
X X X XX X X
X XXX X X X
X X XX X X X
X X X X X X X
X X X X X X X
X X XX X X X
X XX XX XX
X X X X X X X Repeat 13 through 18 from a right spin.
Repeat 7 through 18 from left and right turning flight.
SPIN EVALUATION CONFIGURATION X XX X X XX X
FIGURE 100-1 - SPIN EVALUATION CONFIGURATION MATRIX
101.-105. RESERVED.
Section 9. GROUND AND WATER HANDLING CHARACTERISTICS
106. SECTION 23.231 LONGITUDINAL STABILITY AND CONTROL.
a. Explanation.
(1) For landplanes, §§ 23.231(a) and 23.233 are companion requirements to § 23.75.
(2) For floatplanes, §§ 23.231(b) and 23.233 are companion requirements to § 23.75.
(3) The requirements for both landplanes and floatplanes apply to amphibians.
b. Procedures.
(1) Landplanes should be operated from all types of runways applicable to the type of airplane. Taxi, takeoff, and landing operations should be evaluated for acceptable characteristics. This should include idle power landings as well as landings and takeoffs with procedures used in §§ 23.75 and 23.51.
(2) Floatplanes should be operated under as many different water conditions as practical up to the maximum wave height appropriate to the type of airplane. Taxi (both displacement and step), takeoff, and landing operations should be evaluated for acceptable characteristics.
This includes idle power landings as well as landings and takeoffs with procedures used under §§ 23.75 and 23.51.
(3) Amphibians should be evaluated in accordance with both items (1) and (2) above.
c. Procedures - Multiengine Airplanes. Evaluate all of the considerations contained in paragraph 106b plus the effects of one engine loss during water operations.
d. Airplane Flight Manual (AFM). The AFM should include appropriate limitations plus demonstrated wind and sea state conditions.
107. SECTION 23.233 DIRECTIONAL STABILITY AND CONTROL.
a. Explanation.
(1) Crosswind. This regulation establishes the minimum value of crosswind that must be demonstrated. Since the minimum required value may be far less than the actual capability of the airplane, higher values may be tested at the option of the applicant. The highest 90- degree crosswind component tested satisfactorily should be put in the AFM as performance information. If a demonstrated crosswind is found limiting, it has to be introduced in Section 2 of the AFM.
(2) Ground Loops. Section 23.233(a) does not preclude an airplane from having a tendency to ground loop in crosswinds, providing the pilot can control the tendency using engine power, brakes, and aerodynamic controls. The operating procedures should be placed in the AFM in accordance with § 23.1585(a).
(3) Controllability. Section 23.233(b) is not related to the crosswind requirement of § 23.233(a). The demonstration of compliance with this requirement is accomplished into the wind. The test pilot is searching for any unusual controllability problems during landing and 93
must use judgment as to what constitutes "satisfactorily controllable" since, at some point in the landing rollout, the aerodynamic controls may become ineffective.
(4) Taxi Controllability. Section 23.233(c) requires the airplane to have adequate directional controllability for taxi operations on land for landplanes, on water for floatplanes, and on land and water for amphibians.
b. Procedures.
(1) Crosswind.
(a) The airplane should be operated throughout its approved loading envelope at gradually increasing values of crosswind component until a crosswind equivalent to 0.2 VSO is reached. All approved takeoff and landing configurations should be evaluated.
Higher crosswind values may be evaluated at the discretion of the test pilot for AFM inclusion.
(b) For floatplanes, the use of water rudders or the use of airplane attitude on the water to control weathervaning should be described in the AFM.
(2) Controllability.
(a) A landplane should demonstrate satisfactory controllability during power-off (idle power) landings through landing rollout. This may be conducted into the existing wind and should be evaluated at all key loading envelope points.
(b) Although power-off landings are not expressly required for floatplanes under § 23.233(b), it is recommended they be evaluated.
(3) Taxi Controllability.
(a) A landplane should have sufficient directional control available through the use of nose/tail wheel steering, differential braking (if provided), differential power (multiengine airplanes), and aerodynamic control inputs to allow taxiing at its "maximum demonstrated crosswind" value.
(b) A floatplane should have sufficient directional control available through the use of water rudders, airplane attitude (displacement or plow), taxi technique (displacement or step), differential power (multiengine floatplanes) and aerodynamic control inputs to allow taxiing at its "maximum demonstrated crosswind" value. This is not intended to suggest that all of the above must be evaluated at 0.2 VSO, but accepted techniques using one or more of the above must allow controllable taxiing.
(c) Amphibians should exhibit suitable directional controllability on both land and water in accordance with the preceding two paragraphs. In addition, amphibians should have suitable directional controllability to taxi from the water to a land facility and vice-versa unless prohibited by the operating limitations.
c. Data Acquisition and Reduction. The determination of compliance is primarily a qualitative one. However, wind readings (velocity and direction) should be taken and compared to the wind component chart (Appendix 7) to determine that the minimum 90-degree crosswind component has been tested.
108. SECTION 23.235 OPERATION ON UNPAVED SURFACES.
a. Explanation. This requirement says the airplane landing gear shock absorbing mechanism must function as intended throughout the expected operating envelope of the airplane.
b. Procedures. During the development and certification flight testing, the airplane should be operated on a variety of runways including those considered to be the worst (in terms of roughness) appropriate to the type of airplane. There should be no evidence of damage to the airplane during these operations.
109. SECTION 23.237 OPERATION ON WATER.
Allowable water surface conditions should be established during the certification flight testing, depending on the type of aircraft, to ensure safe operation and attainment of the published takeoff and landing performance.
110. SECTION 23.239 SPRAY CHARACTERISTICS.
a. Explanation. This rule is intended to ensure that any spray produced during water operation neither excessively interferes with the pilot's visibility nor damages, beyond "normal wear-and-tear," the airplane itself.
b. Procedures.
(1) Taxi, takeoff, and landing operations should be conducted throughout the approved loading envelope. Spray patterns should be specifically noted with respect to visibility and their contact areas on the airplane. These areas should be monitored to assure compliance with the rule.
(2) Airplanes with reversing propellers should be demonstrated to comply at the highest reverse power expected to be applicable to the airplane operation.
111.-119. RESERVED.
Section 10. MISCELLANEOUS FLIGHT REQUIREMENTS
120. SECTION 23.251 VIBRATION AND BUFFETING.
a. Explanation.
(1) Flutter. The test required under this section should not be confused with flutter tests, which are required under § 23.629. No attempt is made to excite flutter, but this does not guarantee against encountering it. Therefore, the test should be carefully planned and conducted.
(2) Test Speeds. Prior to the test, the pilot should coordinate with the airframe engineer to determine that the flutter requirements of § 23.629 have been satisfied and to determine the most critical weight and c.g. for the test. The flight test engineer and pilot should obtain from the airframe engineer the dive equivalent airspeed and Mach number to which the test should be conducted. In the absence of a well-calibrated Mach meter, knowing the Mach number and equivalent airspeed, a schedule of pressure altitude and indicated airspeed should be developed for the test.